Lasers are recognized as controllable sources of radiation that is relatively monochromatic and coherent (i.e., has little divergence). Laser energy is applied in an ever-increasing number of areas in diverse fields such as telecommunications, data storage and retrieval, entertainment, research, and many others. In the area of medicine, lasers have proven useful in surgical and cosmetic procedures where a precise beam of high energy radiation causes localized heating and ultimately the destruction of unwanted tissues. Such tissues include, for example, subretinal scar tissue that forms in age-related macular degeneration (AMD) or the constituents of ectatic blood vessels that constitute vascular lesions (e.g., portwine stain birthmarks).
Medical uses of lasers also extend into non-destructive or therapeutic methods (i.e., phototherapy). In these methods, photochemical processes are stimulated in selected tissues. Phototherapy is based on the energy requirements of living cells for normal metabolism and repair. The addition of energy directly to damaged tissues can aid in the return of normal function. In particular, laser therapy (which includes the art recognized terms low energy laser therapy (LELT) and low reactive level laser therapy (LLLT)) can promote healing or desired aesthetic changes (e.g., a reduction in swelling) in targeted tissues, such as damaged muscles and tendons that are often afflicted by pain and/or inflammation.
On cellular and molecular levels, the above therapeutic effects are believed to stem from the ability of chromophores (photoreceptive tissue components) to absorb energy at particular wavelengths. This in turn can initiate or enhance a number of possible biological mechanisms including cell replication, cell metabolism, protein synthesis, adenosine triphosphate (ATP) production, mitochondria replication, phagocytosis, and photodissociation of oxygenated hemoglobin. See Karu, T., THE SCIENCE OF LOW-POWER LASER THERAPY, Gordon and Breach, 1998. Proposed tissue-related activities associated with light absorption include capillary formation, parasympathetic nervous system stimulation, increased endorphin release, increased production and release of adrenal steroids, reduction in pain and in inflammation, reduction of tissue edema, immune system stimulation, enhanced fibroblastic production and collagen synthesis, and accelerated healing of wounds. See Karu, T., Photobiology of Low Power Laser Effects, HEALTH PHYS. May; 56(5): 691-704 (1989).
Therapeutic benefits result from the activation of different photoreceptors that respond to different wavelengths. The energy absorbed by a given tissue depends on the photoreceptive components present, relative to the wavelength used. The absorption of energy by some constituents of virtually all tissues is also a consideration in designing treatment protocols. This is particularly true for therapies (e.g., those involving muscle or joint tissue) where energy must be delivered a significant depth below the skin surface. Water and hemoglobin, for example, are known to absorb specific infrared and visible light wavelengths, respectively, which therefore do not easily penetrate far into the body. The ability of tissues to reflect, absorb, or scatter particular wavelengths at or near the site of energy application also impacts the dose versus depth relationship.